Abstract
The oxidation of H
2S or SO
2 in excess O
2 over Al
2O
3 or TiO
2 (anatase) yields, for either catalyst under anhydrous conditions, an infrared spectrum which is characterized by an intense sharp band near 1380 cm
−1 and a broad band or doublet near 1040 cm
−1. The same spectrum arises from the impregnation of Al
2O
3 with either (NH
4)
2SO
4 or Al
2(SO
4)
3 · 18H
2O or of TiO
2 with (NH
4)
2SO
4 or TiOSO
4 and heating the dried mixture at 450 °C under vacuum. The sulfated surface does not exchange with
18O
2 but does with H
2
18O and only one new shifted high-wavenumber band is produced for partial or complete oxygen-18 exchange. The infrared spectrum changes in the presence of H
2O at 20 °C and resembles that of a more traditional bidentate type sulfate species and we postulate that, in the absence of OH groups or water the sulfate has a structure resembling (
M
3
O
3)
S
O [
M = Al or Ti], whereas in the presence of H
2O or excess surface OH groups this is converted to
▪ type groups, thus accounting for the increased Brønsted acidity. Finally, the sulfated Al
2O
3 surface is more thermally stable and more resistant to reduction in H
2 than is the TiO
2 surface and the ramifications are discussed in terms of the use of these oxides for SO
x
transfer catalysts or in air pollution abatement.